#include"DList.h"  
#include<malloc.h>  
#include<stdlib.h>  
/*分配值为i的节点，并返回节点地址*/  
Position MakeNode(Item i)  
{  
    PNode p = NULL;   
    p = (PNode)malloc(sizeof(Node));  
    if(p!=NULL)  
    {  
        p->data = i;  
        p->previous = NULL;  
        p->next = NULL;  
    }     
    return p;  
}  
/*释放p所指的节点*/  
void FreeNode(PNode p)  
{  
     free(p);  
}  
/*构造一个空的双向链表*/  
DList * InitList()  
{  
    DList *plist = (DList *)malloc(sizeof(DList));  
    PNode head = MakeNode(0);   
    if(plist!=NULL)  
    {  
        if(head!=NULL)  
        {  
            plist->head = head;  
            plist->tail = head;  
            plist->size = 0;  
        }  
        else  
            return NULL;  
    }  
    return plist;  
}  
  
/*摧毁一个双向链表*/  
void DestroyList(DList *plist)  
{  
    ClearList(plist);  
    free(GetHead(plist));  
    free(plist);  
}  
  
/*判断链表是否为空表*/  
int IsEmpty(DList *plist)  
{  
    if(GetSize(plist)==0&&GetTail(plist)==GetHead(plist))  
        return 1;  
    else  
        return 0;  
}  
/*将一个链表置为空表，释放原链表节点空间*/  
void ClearList(DList *plist)  
{  
    PNode temp,p;  
    p = GetTail(plist);  
    while(!IsEmpty(plist))  
    {     
        temp = GetPrevious(p);  
        FreeNode(p);  
        p = temp;  
        plist->tail = temp;  
        plist->size--;  
    }  
}  
  
/*返回头节点地址*/  
Position GetHead(DList *plist)  
{  
    return plist->head;  
}  
  
/*返回尾节点地址*/  
Position GetTail(DList *plist)  
{  
    return plist->tail;  
}  
  
/*返回链表大小*/  
int GetSize(DList *plist)  
{  
    return plist->size;  
}  
  
/*返回p的直接后继位置*/  
Position GetNext(Position p)  
{  
    return p->next;  
}  
  
/*返回p的直接前驱位置*/  
Position GetPrevious(Position p)  
{  
    return p->previous;  
}  
  
/*将pnode所指节点插入第一个节点之前*/  
PNode InsFirst(DList *plist,PNode pnode)  
{  
    Position head = GetHead(plist);  
  
    if(IsEmpty(plist))  
        plist->tail = pnode;  
    plist->size++;  
  
    pnode->next = head->next;  
    pnode->previous = head;  
  
    if(head->next!=NULL)  
        head->next->previous = pnode;  
    head->next = pnode;  
      
    return pnode;   
}  
  
/*将链表第一个节点删除,返回该节点的地址*/  
PNode DelFirst(DList *plist)  
{  
    Position head = GetHead(plist);  
    Position p=head->next;  
    if(p!=NULL)  
    {  
        if(p==GetTail(plist))  
            plist->tail = p->previous;  
        head->next = p->next;  
        head->next->previous = head;  
        plist->size--;  
          
    }     
    return p;  
}  
  
/*获得节点的数据项*/  
Item GetItem(Position p)  
{  
    return p->data;  
}  
  
/*设置节点的数据项*/  
void SetItem(Position p,Item i)  
{  
    p->data = i;  
}  
  
/*删除链表中的尾节点并返回地址，改变链表的尾指针指向新的尾节点*/  
PNode Remove(DList *plist)  
{  
    Position p=NULL;  
    if(IsEmpty(plist))  
        return NULL;  
    else  
    {  
        p = GetTail(plist);  
        p->previous->next = p->next;  
        plist->tail = p->previous;  
        plist->size--;  
        return p;  
    }  
}  
/*在链表中p位置之前插入新节点s*/  
PNode InsBefore(DList *plist,Position p,PNode s)  
{  
    s->previous = p->previous;  
    s->next = p;  
    p->previous->next = s;      
    p->previous = s;  
  
    plist->size++;  
    return s;  
}  
/*在链表中p位置之后插入新节点s*/  
PNode InsAfter(DList *plist,Position p,PNode s)  
{  
    s->next = p->next;  
    s->previous = p;  
      
    if(p->next != NULL)  
        p->next->previous = s;  
    p->next = s;  
      
    if(p = GetTail(plist))  
        plist->tail = s;  
      
    plist->size++;  
    return s;  
}  
  
/*返回在链表中第i个节点的位置*/  
PNode LocatePos(DList *plist,int i)  
{  
    int cnt = 0;  
    Position p = GetHead(plist);  
    if(i>GetSize(plist)||i<1)  
        return NULL;  
  
    while(++cnt<=i)  
    {  
        p=p->next;  
    }  
  
    return p;  
}  
  
/*依次对链表中每个元素调用函数visit()*/  
void ListTraverse(DList *plist,void (*visit)())  
{  
    Position p = GetHead(plist);  
    if(IsEmpty(plist))  
        exit(0);  
    else  
    {  
          
        while(p->next!=NULL)  
        {  
            p = p->next;  
            visit(p->data);            
        }         
    }  
} 
